The present invention, in some embodiments thereof, relates to hematopoietic precursor cells mobilization.
The forced migration of hematopoietic stem/progenitor cells (HSPC) from the bone marrow (BM) into the peripheral blood (PB), termed mobilization, is important from a clinical point of view as a procedure that allows for the collection of HSPC for transplantation.
Many agents have been described that induce mobilization of HSPC. Granulocyte-colony stimulating factor (G-CSF), most frequently employed in the clinic, efficiently mobilizes HSPC after a few consecutive daily injections. Other compounds, such as polysaccharides (e.g., zymosan), mobilize HSPC within 1 hour after a single injection. Mobilization can also be induced by chemokines (e.g., IL-8, Gro-β), growth factors (e.g., vascular endothelial growth factor) and CXCR4 antagonists (e.g., AMD3100) and is modulated by lipopolysaccharide that is released by intestinal bacteria. Unfortunately, about 25% of patients do not respond efficiently to currently recommended mobilization protocols and are termed poor mobilizers.
The molecular mechanisms governing the mobilization of HSPC are still not well understood. It was previously shown that expression of the G-CSF receptor (G-CSFR) on hematopoietic progenitor cells (HPCs) is not required for their mobilization into the peripheral blood in response to G-CSF. This observation suggests that G-CSF induces HPC mobilization indirectly through the generation of trans-acting signals. Moreover, accumulating evidence suggests that attenuation of the α-chemokine stromal derived factor-1 (SDF-1)-CXCR4 axis, which plays a pivotal role in retention of HPCs in the BM, results in the release of these cells from the BM into the PB.
It has been demonstrated that a highly proteolytic microenvironment is induced in the bone marrow during HPC mobilization by G-CSF [Levesque et al., Exp Hematol (2002) 30(5):440-9]. In particular, matrix metalloproteinase-9 (MMP-9 or gelatinase B), neutrophil elastase (NE), and cathepsin G (CG) accumulate in the bone marrow of mice during treatment with G-CSF with kinetics that mirror HPC mobilization. Some recent studies suggest that hematopoietic proteases released by neutrophils into the bone marrow microenvironment may play a role in HPC mobilization. Neutrophils express 3 serine proteases: NE, CG, and proteinase 3. These proteases are stored in primary granules of neutrophils and can be released following neutrophil activation [Borregaard and Cowland, Blood. (1997) 89(10):3503-21].
An additional known serine protease is thrombin, a 37 kDa protease well known for its role in the blood coagulation cascade. Thrombin is capable of signaling through Protease-activated receptors PARs, which are expressed throughout the body and are known to be involved in vascular responses, embryonic development and malignancies. PARs belong to a family of G-protein-coupled receptors that undergo N-terminal cleavage to reveal a tethered ligand. It has been shown that NE, CG, and PR3 cleave PARs at distinct sites from thrombin and inhibit subsequent thrombin-induced activation of the receptors [Renesto et al., Blood. (1997) 89(6):1944-53; Sambrano et al., The Journal of biological chemistry. (2000) 275 (10): 6819-23].
U.S. Patent Application No. 20080305097 describes the use of cathepsin K (CTK), a cysteine protease, or a cathepsin K inhibitor (CTKI) for stem cell mobilization. Specifically, U.S. Patent Application No. 20080305097 teaches methods of inducing mobilization of stem cells from the bone marrow to the peripheral blood by the use of CTK or, alternatively, methods of increasing retention of stem cells in the bone marrow by the use of CTKI. According to the teachings of U.S. Patent Application No. 20080305097, CTK is capable of specifically inhibiting SDF-1 activity and thereby effecting stem cell mobilization.